Potentiometer device



Dec. 17, i935. J. H. CLARK POTENTIOMETER DEVICE Filed June 13, 1935 Patented Dec. `T17, 1935 UNI TED STATES '2,024,275 roTENTIoME'rER l.DEVICE Jean 'Harold Clark, El Monte, QCalif., `Yassigner .to AmericanTelephone and Telegraph Company, New York, N. Y., aA corporation of NewYork .Application June 13, 1935, SerialjNo. 26,510

-6 Claims.

This invention relates to improvements in potentiometer devices, and morezparticularlysto a potentiometer devicewhich will .have a constant impedanceregardless of variations in-:the settings or adjustments thereof duringits operation.

Inpotentiometer deviceszofthe prior art variations `in voltages produced by the potentiometer have also involved changes .in the impedance of the potentiometer. Accordingly, one of the primary objects of the Ainvention .is .to provide a potentiometer whichwill present a constant impedance regardless of .variations in voltagesproduced by the device itself. In the arrangements of lthe invention this is accomplished by connecting acrosspthe potentiometer circuit on Vone side cf the Lvoltage source a plurality of-resistances or impedances. To vchange the .voltage produced by the potentiometer any .desirednumbenof :these resistances would Vbe shifted toa position across the potentiometer circuit,.buton i:the other side of the voltage source. .As the number of resistances .or impedance `elements connectedfacross4 the circuit will always be the same after theshifting.

'as before, the device will present a constant rimby contact'resistance, changes in temperature,4 or

inaccuracy in construction, `introduceless error than .in the usual type .of Vdevice .heretofore used.

The device of the invention has :the .further advantage that all contacts are wet evenwhen it is supplying no output current.

The Vinvention may be more fully understood from the followingidescription .together with the accompanying drawing in the Figures .1, la, .2, 2a, 3 and 4 of which the invention is illustrated. Figs. 1 andila are vschematicgdiagrams of` potentiometer.devicesofithepriorart. Figs. 2, 2a-and 3 areschematic :diagrams of the'potentiometer device ofgthisinvention. .Fig.4 is a circuit diagram illustrating :.one mannerin .which .the device of the inventionz'mayibe altilized. Similarlreference charactershave.- beenutilized to. denote like parts in .allof .thezflgnres In Fig. 1 is shown schematically afconventional type potentiometer .deviceofithe .prior ar-t which supplies .an .external voltage across theV points b, c of 10 rvoltsand has .an internal impedance Voi! fohms, looking in the direction of the arrow. 11n Fig. la. thesame potentiometer is shown adjusted to supply '5 volts across the points b', c. Y It will be seensthatin .this .case the internal vimpedance lookingin .the direction of the arrow will tbe 3 ohms. In other Words, with .the conventional type potentiometer of the prior-art the variation in the voltagesupplied thereby Will result in a change in :the internal impedance of .the device. Fig..2 .is a schematic showing of a potentiometer embodying the principles of this inventionand supplying an external voltage across the points d, f of 10 volts, with an internalimpedance of `1 ohm .looking inthe direction of the arrow. The resistanceof the .voltage sourceein Fig. 21is considered negligible. Fig. Zashows schematically the 2 same potentiometer. device of I the invention 'as shown in Fig. '.2 vbut adjusted to supply "5 volts across thepoints d', f. It will appear fromhthe diagram that .the internal impedance looking-in the .directionof the arrow will be the same asbefore,.name1y, 1:ohm. In other words, with the potentiometerdevice o'f thisinvention 'an-adjustment l.thereof to .produce a-diierent voltage will not result inachange in the Ainternal impedance of the. device.

lInFig. 3 there is-shown schematically the general conditionslfor the Vconstant impedance potentiometer of this invention. Assume afsource ofipotentialjE, .having a negligible internal resistance, inacircuithaving a total| number =of equal `resistors R arranged as shown. Then the internal impedance ofthe circuit-looking inthe direction of the arrow as represented at points A, .iBis l.independent` of `the Idistribution of the R resistors on the tvv-o .sides of Efandfthe voltage suppliedatrthepoints A, B isin direct proportion to :the numbervof R resistors-connected-on the lef-t side.` of E.

Internal resistance R iInfFig. 4- is-shown a -ci-rcuitdiagramillustrating how the potentiometer device could be utilized'in a-system orrecordingthe number of l,telephone lines in a group in use simultaneously. `VFor example; eachof thestelephone lines might-have'associated-with ita relayfsuch as ,the ,relays F. 'When any'line kwas vinuse its associated 'relay' would: be causeclfto operateand change `the'voltage proy tion of slider S.

duced by the potentiometer. These changes in voltage could be utilized to determine the number of lines in use. The potentiometer device would comprise a pair of conductors, one of which would include the source of voltage E. Normally there would be bridged across these conductors on the right hand side of source E a plurality of resistors R, one for each of the number of telephone lines in the group under supervision. When none of the lines was in use and none of the F relays operated, all oi the resistors R would be bridged across the conductors on the right hand side of source E and the device would be idle. Whenever one or more of the telephone lines were in use and its associated F relay operated, one or more of the resistors R would have its connection shifted so that it would be connected across the potentiometer conductors on the left hand side of source E. As pointed out heretofore with respect to Figs. 2, 2a and 3, this would result in a change inthe voltage applied from source E to the terminals of the conductors without any change in the internal impedance of the device.

As heretofore pointed out, these changes in voltage applied to the terminals of the potentiometer conductors may be utilized to determine the number of busy telephone lines under supervision. For this purpose a measuring device would be provided at the terminals of the conductors. For purposes of illustration this device is shown as a potentiometer recorder of a type well known in the art. This would include a 200 ohm slide-wire potentiometer P, the slider S of which might be automatically adjusted by the recorder mechanism (not shown) to such a value as will balance the galvanometer G. The record might be made by a moving pen on a paper chart or tape, the position of the pen on the tape being determined by the position of the potentiometer slider S. In the circuit shown the operation of the meter depends upon unbalanced voltages between the two potentiometers rather than upon the principle of the Wheatstone bridge. The galvanometer G is connected between the two potentiometers and the current in it reduced to zero by the opera- However, other types of measuring devices than the specific oneshown may be utilized to measure the changes in voltage produced by the constant impedance potientometer device of the invention, if desired.

In the arrangements shown in Fig. 4 there are also provided means for compensating for changes in the impedance of the potentiometer device of the invention by adding to or taking away therefrom certain of the resistors R. These means are the resistance unit H which is adjustable by the switch S and which is connected across the conductors of the potentiometer device. Obviously, any increase in a given number of therR resistors, shown for purposes of illustration as 9000 ohms each, will decrease the internal impedance of the device. Also, any decrease in the number of these R resistors will increase the internal impedance. Compensation for this may be made by adjusting Switch S to the proper stepy on resistance H. For example, in the arrangement shown, resistors R can be provided in multiples of 20 up to 100, and proper compensation for any number of resistors less than 100 is obtained by setting switch S on the proper step of resistance H. This will be clear :from the following:

For convenience the impedance of the potentiometer with a varying number of resistors is to be held at, say, ohms. This is its impedance with resistors of 9000 ohms each. It may be step 80.

noted that the adjustment of switch S for this condition opens the circuit for the shunt resistance H. When only 80 resistors are to be used, since the impedance of these is 112.5 ohms, 450 ohms is placed in parallel to obtain the desired 5 .9o-ohm impedance by adjusting the switch S to The total resistance of H which is 450 ohms is connected in shunt on this step. The parallel combination of 112.5 ohms and 450 ohms is 90 ohms. When 60 resistors are to be employed 10 having an impedance of 150 ohms resistance H is to be adjusted to 225 ohms by setting switch S to step 60. The parallel combination of 150 ohms and 225 ohms is 90 ohms. For 40 resistors of 225 ohms impedance a shunt of 150 ohms is used. For 15 20 resistors of 450 ohms impedance a shunt of 112.5 ohms is used.

In the above described arrangements the impedance elements referred to as the resistors R may consist either of resistance, of capacity, or, 20 of inductance. Furthermore, the voltage utilized and designated as E might, if desired, be alternating current derived from a low impedance source. Also, the impedance elements might obviously be designed to change the output by frac- 25 tional amounts so that variation in decibels or in steps of .1, .01, .001, might be obtained.

The arrangements of the invention might, if desired, be used as a voltmeter multiplier by connecting a low resistance meter movement in place 30 of the voltage source, thus securing diierent voltage scales while the impedance of the voltmeter remains substantially constant.

It is pointed out that one of the reasons for desiring the constant impedance device, such as 35 that of the invention, is that when it is connected to a circuit of substantially constant impedance, the current in the circuit is varied in accordance with the setting of the potentiometer. The device is thus useful for Calibrating meters. 40 For pyrometric work with a thermocouple, or for electrometric titration, the sensitivity of the meter or the impedance of the potentiometer may be adjusted by means of a rheostat so that a variation of one step on the potentiometer wil change the meter reading an integral number of divisions such as 10, 20, 50 or 100, when the meter reading may be used directly for interpolation. This is a considerable improvement over the present methods, both in speed and in the cost of the 50 equipment required for the same accuracy in results. A plug box type of potentiometer using steps of .1, .2, .2, .5, .01, .02, .02, .05, etc., could be constructed providing variations from .0001 to 1.0000 by ten thousandths and requiring only 16 55 impedance elements.

Accordingly, while the invention has been disclosed as embodied in certain specific arrangementsV which are deemed desirable, it is understood that it is capable of embodiment in many 60 and other widely varied forms without departing from the spirit of the invention as dened by the appended claims.

. What is claimed is:

1. ,A potentiometer device comprising a cir- 65 cuit including a source of potential and a measuring device included in said circuit, a plurality of impedances bridged across said circuit, and means to shift the connections of said impedances from one terminal of said source to the 70 other terminal of said source without changing the impedance looking into said circuit from said measuring device.

2. A potentiometer device comprising a. pair of one of said conductors, a plurality of impedances bridged across said conductors, and means to shift the connections of any number of said impedances from one side of said source to the other side of said source Without changing the impedance measured across said conductors.

3. A potentiometer device comprising a pair ci conductors, a source of voltage included in one of said conductors, a plurality of impedances bridged across said conductors, and means to shift the connections of any number of said impedances from one side of said source to the other, whereby the Voltage applied from said source across the terminals of said conductors may be changed without changing the impedance measured across the terminals of said conductors.

4. A potentiometer device comprising a pair of conductors, a source of voltage included in one of said conductors, a plurality of impedances bridged across said conductors, means to shift the connections of any number of said impedances from one side of said source to the other side of said source, whereby the voltage applied from said source across the terminals of said conductors may be varied Without changing the impedance measured across said conductors, and a variable resistance device bridged across said conductors to compensate for any increase or decrease in the number of said impedance devices connected across said conductors.

5. A potentiometer device comprising a pair of conductors, a source of voltage included in one of said conductors, a plurality of impedances bridged across said conductors, means to shift the connections of any number of said impedances from one side of said source to the other side of said source, whereby the voltage applied from said source across the terminals of said conductors may be varied Without changing the impedance measured across said conductors, a variable resistance device bridged across said conductors to compensate for any increase or decrease in the number of said impedance devices connected across said conductors, and a measuring device connected across said conductors for measuring changes in the voltage applied across the terminals of said conductors.

6. A potentiometer device comprising a pair of conductors, a source of voltage included in one of said conductors, a plurality of impedances normally bridged across said conductors on one side of said source of voltage, and a. plurality of relays individual to each of said impedances whereby the connections of any number of said impedances may be shifted from the side of said source of voltage to which they are normally connected to the other side of said source for changing the voltage applied from said source across the terminals of said conductors without changing the impedance measured across said conductors.

JEAN H. CLARK. 

